Petroleum refiners often produce desirable products such as turbine fuel, diesel fuel, middle distillates, naphtha, and gasoline, among others, by hydroprocessing a hydro-carbonaceous feedstock derived from crude oil or heavy fractions thereof. Hydroprocessing can include, for example, hydrocracking, hydrotreating, hydrodesulphurization and the like. Feedstocks subjected to hydroprocessing may include vacuum gas oils, heavy gas oils, and other hydrocarbon streams recovered from crude oil by distillation. For example, a typical heavy gas oil comprises a substantial portion of hydrocarbon components boiling above about 371° C. (700° F.) and usually at least about 50 percent by weight boiling above 371° C. (700° F.), and a typical vacuum gas oil normally has a boiling point range between about 315° C. (600° F.) and about 565° C. (1050° F.).
Hydroprocessing concerns reacting the feedstock in the presence of a hydrogen-containing gas with suitable catalyst(s) to convert constituents of the feedstocks to other forms, to extract contaminants from feedstock, etc. In many instances, hydroprocessing is accomplished by contacting the selected feedstock in a reaction vessel or zone with the suitable catalyst under conditions of elevated temperature and pressure in the presence of hydrogen as a separate phase in a substantially three-phase system (i.e., hydrogen gas, a substantially liquid hydrocarbon stream, and a solid catalyst). Such hydroprocessing apparatuses are commonly undertaken in a trickle-bed reactor where the continuous phase throughout the reactor is gaseous.
Many reactor systems comprise multiple beds of catalyst and many employ multiple reactors. Due to the nature of the reactions, temperature control of the reactors and the catalyst beds is important.